This invention relates to a system for printing images having a plurality of gradation levels, which, in the case where printed images, such as pictures, letters, and characters, are reproduced by using picture element reproduction elements, permits the reproduction of intermediate gradation levels or half tones of the printed images.
In order to reproduce or print images such as pictures, letters, and characters from input information, a method has been proposed. In accordance with the proposed method input images are divided into a number of very small cells (called picture elements hereinbelow) arranged in matrix form and each of the printed images is obtained as a whole by using picture element reproduction elements, one each of which being disposed so as to correspond to a different picture element. In general, according to this method, in most cases, logic circuits such as digital integrated circuits are used in electric circuits driving picture element reproduction elements. Such a reproduction system has a drawback that, since each picture element reproduction element can give only two value information, i.e. ON or OFF, corresponding to the presence or absence of an information signal, it can express only a black and white picture element. Therefore, printed images having a half tone or a plurality of gradation levels cannot be reproduced. In such a case, if a picture element were further divided into still smaller elements and considered as an assembly of the still smaller elements in a certain area, gradation display of printed images would be possible by this prior method. However, this prior method has other disadvantages in that the distinctness or resolving power for the printed images is degradated, that a picture element reproduction system should be constituted extremely finely, and that the structure of its hardwares are complicated.